(1) Field of the Invention
Electric timing controls for equipment for drying of laundry such as linens, clothing and other fabrics.
(2) Description of the Prior Art
Typical large capacity commercial apparatus (in the 50 to 400 pounds per load range) for drying washed bedding, towelling, cleaning rags, work uniforms and the like are either gas-oil fired or steam heated. In order to reduce the wasting of fuel, i.e., to utilize fuel or steam heat most effectively, the heating system of the dryer must be controlled to a finer degree than has been practised heretofore.
In a common type of steam-heated dryer the drying cycle is arbitrarily terminated solely by a manually preset timer, which may either initiate an audible device to prompt manual turnoff, or automatically turn off the heating means. In some systems this event may effect bypassing of air around the steam coils and the blower later is turned off by running of a second manually preset timer during a cooling cycle. In gas or gas/oil fired dryers, a high flame first raises the air temperature to a predetermined temperature at a fast rate, and low flame takes over until a manually preset timer arbitrarily shuts off the heat. (The heat and low flame can be modulated automatically in response to temperature sensing until the timer winds down.)
Ineffective utilization of energy occurs either when the machine operator determines that the load is not sufficiently dry at the end of a batch cycle and therefore restarts the cycle, or when the load was sufficiently dry long before the machine heating cycle was terminated--both of these situations waste energy. One cause of either such condition is the reliance on human judgement, either in setting the time and/or temperature limits, or in other respects, such as by incorrectly estimating the weight or moisture content of the load. it is an object of this invention to provide a dryer control system in which the optimal amount of energy is applied to bring the load to its desired final state of dryness, or moisture content.